1. Field of the Invention
This invention relates generally to the field of fault classification in an industrial process and, more particularly, to a method and apparatus for fault classification based on residual vectors.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the quality, reliability and throughput of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for higher quality computers and electronic devices that operate more reliably. These demands have resulted in a continual improvement in the manufacture of semiconductor devices, e.g., transistors, as well as in the manufacture of integrated circuit devices incorporating such transistors. Additionally, reducing the defects in the manufacture of the components of a typical transistor also lowers the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
The technologies underlying semiconductor processing tools have attracted increased attention over the last several years, resulting in substantial refinements. However, despite the advances made in this area, many of the processing tools that are currently commercially available suffer certain deficiencies. In particular, such tools often lack advanced process data monitoring capabilities, such as the ability to provide historical parametric data in a user-friendly format, as well as event logging, real-time graphical display of both current processing parameters and the processing parameters of the entire run, and remote, i.e., local site and worldwide, monitoring. These deficiencies can engender nonoptimal control of critical processing parameters, such as throughput, accuracy, stability and repeatability, processing temperatures, mechanical tool parameters, and the like. This variability manifests itself as within-run disparities, run-to-run disparities and tool-to-tool disparities that can propagate into deviations in product quality and performance, whereas an ideal monitoring and diagnostics system for such tools would provide a means of monitoring this variability, as well as providing means for optimizing control of critical parameters.
Semiconductor devices are manufactured from wafers of a semiconducting material. Layers of materials are added, removed, and/or treated during fabrication to create the electrical circuits that make up the device. The fabrication essentially comprises four basic operations. Although there are only four basic operations, they can be combined in hundreds of different ways, depending upon the particular fabrication process.
The four operations typically used in the manufacture of semiconductor devices are:                layering, or adding thin layers of various materials to a wafer from which a semiconductor device is produced;        patterning, or removing selected portions of added layers;        doping, or placing specific amounts of dopants in the wafer surface through openings in the added layers; and        heat treatment, or heating and cooling the materials to produce desired effects in the processed wafer.        
Occasionally, during the fabrication process, one or more process steps are not performed as expected on a production wafer. Such conditions may be due to an error in the fabrication facility automated work flow system (e.g., a database or control script error), a tool failure, or an operator error. If the abnormal process steps occur early during the fabrication process, it is not uncommon for the faulty wafer to undergo many subsequent steps prior to the faulty fabrication being identified. Once a fault is identified further processing is often necessary to determine the nature or cause of the fault, unless the fault is grossly obvious. This process is typically referred to as fault classification. Fault classification may be time consuming and may require significant human intervention. Improved fault classification increases the response time for correcting defect conditions.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.